1. Field of the Invention
The invention relates to a device for the electrical connection of at least two structural elements which are disposed on the steering wheel axis of a motor vehicle and rotatable with respect to each other.
2. Description of the Prior Art
There are devices for the electrical connection between electrical parts which can rotate with respect to each other in motor vehicles, for example, required for the transfer of electrical signals from stationary structural parts attached at the vehicle-chassis to electrical devices arranged on the steering wheel. In the known arrangements, an electrical connection is effected between the battery of the vehicle and the switch of the horn mounted on the steering wheel by means of concentric contact elements at one part, and by slip-rings or contact brushes on the other part, whereby an electrical connection is provided during rotation. Electrical connecting devices of this type suffer from relatively high wear, and have the disadvantage, that they cause disturbing noise during their rotation. Furthermore, in such devices with sliding contact elements, relatively high electrical transfer resistances are encountered. A high transfer resistance is acceptable at electrical switching- or signal devices, in which-for example, when blowing the signal horn - relative large currents flow in the electrical connection line. However, such a connecting device is not acceptable for the cases where maximum contact reliability is the decisive factor, or in situations where only very small currents of only a few mA flow in the connection line, for example for test or control purposes, such as the electrical or electronic monitoring of the safety system of a vehicle. The explained known device is not suited for safety reasons for a vehicle-safety system, wherein an airbag serving as impact-protection for the passengers is fastened to the steering wheel, and the airbag is provided with an electrical ignition device, which is connected with an electrical sensor in the vehicle-chassis through an electrical connection, where the electrical sensor, in case of a crash, is activated and operates the ignition device, which in turn causes the airbag to inflate. It is desirable that this safety system be continuously monitored to indicate its readiness to operate. For this purpose an electrical control current of only a few mA flows continuously in the electrical connection system, to make certain that in an emergency the ignition device, for example a pyrotechnical charge, is reliably ignited.